324 THE ANATOMY OF INVERTEBRATED ANIMALS. 



one pair of antennary organs completely suppressed. Upon 

 this view, the eye-bearing shield is a carapace covering a 

 cephalo-thorax, into which the two anterior thoracic somites 

 only enter. These are followed by six free thoracic somites, 

 the four posterior of which are pulmoniferous. But no trace 

 of the supposed missing antennary appendage has been met 

 with in the embryonic condition, so that the alternative pos- 

 sibility that the mouth is situated one somite farther forward 

 in the Scorpion than in the Crustacean must be borne in mind. 

 It is a very interesting fact that Metschnikoff ! has found ru- 

 diments of limbs on those somites of the embryo Scorpion on 

 which the stigmata are situated — a circumstance which sug- 

 gests the suspicion that the Scorpion is derived from some 

 form possessing more numerous limbs. 



The minute oral aperture leads into a small pyriform lat- 

 erally-compressed sac (Fig. 86, a) with chitinous elastic walls. 

 Muscles pass from these to apodemes of the sternal wall of 

 the head, and doubtless act as divaricators of the wall of the 

 sac. As the Scorpion sucks out the juices of its prey, it is 

 probable that the elastic sac acts as a kind of buccal pump — 

 the nutritious fluid rushing in when the sides of the pump are 

 separated, and being squeezed into the oesophagus when the 

 elasticity of the walls brings them back to their first position. 2 



The oesophagus (Fig. 86, b) is an exceedingly narrow tube, 

 which springs from the tergal and posterior aspect of the sac 

 just mentioned, traverses the nervous ring, and then, passing 

 obliquely upward and backward, enlarges into a dilatation 

 which receives the secretion of two large salivary glands, by 

 a wide duct' on each side. The alimentary canal narrows 

 again, and, becoming a delicate cylindrical tube which widens 

 posteriorly, passes straight through the body to the anus. 

 The numerous ducts of the liver open into the anterior part 

 of this region of the alimentary canal, and it receives two 

 delicate Malpighian tubuli. 



The liver is a vast follicular gland, which occupies all the 

 intervals left between the other organs in the enlarged part 

 of the bodv, and even extends for some distance into the nar- 

 row posterior somites. 



The eight-chambered heart (Fig. 86, H) is a larger and 

 more conspicuous structure than the alimentary canal, above 

 which it lies, in a pericardial sinus situated in the middle 



1 " Embryologie des Scorpions." ( ' Zeitschrift fur wiss. Zoologie, 1871.) 



2 Huxley, " On the Mouth of the Scorpion." (Quarterly Journal of Micro- 

 scopical Science, 1860.) 



